Neutron Resonance Absorption Spectroscopy Research Articles

Optimization of Moderator Size of Thermal and Epithermal Neutron Source Based on a Compact Accelerator for Neutron Imaging

A compact accelerator-driven neutron source has some advantages over a large accelerator facility in terms of accessibility and usability. Recently, the project to develop a non-destructive testing system for nuclear fuels by neutron imaging using a compact accelerator-driven neutron source has launched in Japan. In this project, the traditional neutron radiography and temperature imaging by neutron resonance absorption spectroscopy (N-RAS) have been studied. From the viewpoint of L/D, a high-brightness moderator is desirable for the neutron imaging. In this study, we investigated the dependence of moderator size on the source brightness and the pulse characteristics of the neutron by simulation calculations to design the moderator for imaging using thermal and epithermal neutrons. As a result, the optimal size of the moderator for the neutron imaging was 6∼7cm in the energy region from 5 meV to 100eV.

Spatial resolution of a [formula omitted] neutron imaging detector

We present a detailed study of the spatial resolution of our time-resolved neutron imaging detector utilizing a new neutron position reconstruction method that improves both spatial resolution and event reconstruction efficiency. Our prototype detector system, employing a micro-pattern gaseous detector known as the micro-pixel chamber (μPIC) coupled with a field-programmable-gate-array-based data acquisition system, combines 100μm-level spatial and sub-μs time resolutions with excellent gamma rejection and high data rates, making it well suited for applications in neutron radiography at high-intensity, pulsed neutron sources. From data taken at the Materials and Life Science Experimental Facility within the Japan Proton Accelerator Research Complex (J-PARC), the spatial resolution was found to be approximately Gaussian with a sigma of 103.48±0.77μm (after correcting for beam divergence). This is a significant improvement over that achievable with our previous reconstruction method (334±13μm), and compares well with conventional neutron imaging detectors and with other high-rate detectors currently under development. Further, a detector simulation indicates that a spatial resolution of less than 60μm may be possible with optimization of the gas characteristics and μPIC structure. We also present an example of imaging combined with neutron resonance absorption spectroscopy.

Accelerator-based neutron tomography cooperating with X-ray radiography

Abstract Neutron resonance absorption spectroscopy (N-RAS) using a pulsed neutron source can be applied to time-of-flight (TOF) radiography, and the obtained parameters from the peak shape analysis can be reconstructed as the tomograms of nuclide distributions using computed tomography (CT). The problem is that the available spatial resolution is not sufficient for radiography imaging. In this study, we combined neutron and X-ray radiographies to improve the quantitative reconstruction of the neutron tomogram. The accelerator-based neutron source emits X-rays (or gamma-rays) at the same time the neutron pulse is emitted. We utilized the X-ray beam from the neutron source to obtain X-ray radiogram on the same beam line with neutron radiography and then reconstructed the neutron tomogram quantitatively with the help of a detailed sample internal structure obtained from the X-ray radiogram. We calculated the nuclide number density distribution tomogram using a statistical reconstruction procedure, which was easy to include in the structure model during the reconstruction. The obtained result of nuclide number density distribution showed good coincidence with the original object number density.

Epithermal neutron tomography using compact electron linear accelerator

Neutron resonance absorption spectroscopy (N-RAS) with a pulsed neutron source can distinguish the dynamics of individual nuclides having resonance peaks on epithermal neutron region. The analyzed internal information of nuclide presence and its effective temperature can be reconstructed as distributions over the object cross-section using computed tomography (CT). Because some of the resonance absorption cross-sections have very large values, N-RAS could match the small neutron pulsed source by its high sensitivity. In this study, we have constructed a new instrument of N-RAS on a compact electron linac neutron source. Resonance absorption measurements and CT imaging with the instrument have succeeded for some kinds of nuclide.

Pulsed neutron imaging using resonance transmission spectroscopy

We are developing the energy-selective neutron radiography and tomography technique by using the pulsed neutron source and the time-of-flight (TOF) spectroscopy. Neutron resonance absorption spectroscopy with computer tomography, N-RAS/CT, can non-destructively give the tomographic image indicating material information such as nuclide, density and temperature inside the object. The primary N-RAS/CT was performed by detecting prompt γ-rays emitted from nuclei absorbing neutrons as a function of neutron TOF. In this case, position dependent data need to be obtained by scanning the object with a moving slit. On the other hand, in this paper, we propose a new N-RAS/CT method using neutron transmission spectroscopy combined with 2-dimensional position sensitive neutron detector (2d-PSND), which is applicable to TOF measurement. The greatest feature of this method is shorter measurement time than the previous one because 2d-PSND can obtain spatial information at once. For this reason, we carried out the new N-RAS/CT experiment to examine its feasibility at the pulsed neutron facility based on the small accelerator.

Simulation for neutron resonance absorption spectroscopic tomography

We are developing the pulsed neutron imaging technique using the time-of-flight (TOF) spectroscopy. Neutron resonance absorption spectroscopy (N-RAS) can identify individual nuclides, deduce its density and study its dynamics by analyzing energy, intensity and Doppler broadening of each resonance absorption peak. N-RAS/ computer tomography (CT), which is N-RAS combined with CT, can non-destructively show the tomographic image indicating the distribution of resonance nuclide and its dynamics inside various materials. However, large resonance absorption cross-section frequently causes the self-shielding effect, distorting the reconstructed CT image. Therefore, in the previous experiment, we obtained a reconstructed CT image different from the real distribution of resonance nuclide, using a data processing method without the self-shielding correction. For this reason, we have proposed a new data processing method to correct the self-shielding effect for N-RAS/CT, and carried out Monte-Carlo simulations to examine the feasibility of this method. As a result, we have succeeded in establishing a procedure that produces the undistorted CT image, indicating the absolute value of resonance nuclide density.

Energy sliced neutron tomography using neutron resonance absorption spectrometer

Neutron tomography was studied using a neutron resonance absorption spectrometer installed on a pulsed neutron source. The neutron resonance absorption spectroscopy (N-RAS) is a method to study the dynamics of nuclides by analyzing the Doppler broadening of their resonance spectra. N-RAS can combine with the computer tomography (CT) technique to obtain the tomogram of an object. We developed the CT reconstructions which were repeated at each time-of-flight (TOF) channel and piled up the reconstructed images in order to make the resonance spectrum over the wide energy range. Finally, we could deduce the information of nuclides and its temperature distributions in the sample non-destructively. We call this new TOF tomography technique as neutron resonance imaging (NRI).

Remote-sensing, Non-destructive, and Computed-tomography-assisted Thermometry by Neutron Resonance Absorption Spectroscopy

We applied the method of neutron resonance absorption spectroscopy to thermometric measurements of a bulk object. Through an analysis of the resonance absorption spectrum of imbedded neutron-absorbing nuclides, the “effective temperature”, which coincides with the actual local temperature near and above room temperature, can be determined. If a thermal gradient exists, computed tomography techniques could be used in conjunction with the analysis for a reconstruction of the temperature distribution over a planar cross-sectional area. We find that the experimental data agree with the temperature profile calculated from the heat conduction equations. The measurements were carried out using the neutron resonance absorption spectrometer DOG of KENS, Japan. The overall results demonstrated the feasibility of this method for industrial applications where remote-sensing and non-destructive temperature mapping of bulk objects is necessary.

Computer tomography thermometry—an application of neutron resonance absorption spectroscopy

Neutron resonance absorption spectroscopy (N-RAS) associated with computer tomography was applied to thermometry for an inhomogeneous bulk object. This new method provides two-dimensional distributions of nuclide temperatures on the planar cross-section of an object as information from remote-sensing analysis. The experimental result showed good agreement with the actual temperature distribution inside the object, and the simulation of the experiment correctly reproduced the result. For greater accuracy, we need to achieve finer spatial resolution and better statistical reliance on N-RAS. The development of this novel approach has links to new industrial applications utilizing neutrons for remote sensing and non-destructive thermometry.

Neutron resonance absorption spectroscopy on ionic conductor AgI

The neutron resonance absorption experiments were performed on an ionic conductor AgI and a reference sample Ag-metal, and the effective temperatures were obtained in a wide temperature range of 20–300 K. The obtained effective temperatures in Ag-metal agree well with the calculated values from its characteristic Debye temperature of θ D=225 K. In AgI an anomaly is found around 150 K where the Debye temperature of Ag-atom changes from θ D=160 to 440 K, while nothing can be seen in that of I-atom.